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  #31 (permalink)  
Old 04-05-2009, 09:05 AM
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what grit does the factory use? I once knew a guy soooo cheap ,he saved his 320 and 400 wet paper to color sand. It worked for him but I quit when he expected me to do the same.So the answear I think your looking for is yes the grit gets finer and doesnt just disappear.when I sand I switch when it stops cutting its only 600 till that point ,then I breeze over everything with 800 quickly,always keeping freash paper,it dont go far either.Adhesoin is important,THE most important part of the paint biz and your right to give it much thought it shows a true craftsman you should always ask why and question everything not going blindly the way you were taught,if you were taught wrong you will always be wrong.youre on the right track

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  #32 (permalink)  
Old 04-06-2009, 05:24 AM
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Keep in mind that most of todays papers are "P" grade, which are
more coarse than yesterday papers without the "P" designation.

P600 is actually more coarse than the old regular 400 grit papers.
P600 is about 380 grit on the old scale.
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  #33 (permalink)  
Old 04-10-2009, 03:59 PM
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I am no paint expert, but jcclark brings up a good point. Sorry to keep talking about grit. But are we talking P600 or the old US 600. Big difference. See link for comparison.

http://www.bowlingtracker.com/forums...6&d=1179781172
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Old 04-10-2009, 05:46 PM
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good point,I noticed today my sandpaper was p400 and p600 it got me wondering, to tell you the truth I never noticed a differance in sanding or in the finished ,painted product ,so I called the paint store and asked then he asked someone else and so on finally the answear was theres no differance. I really cant tell but p400 can be painted without a sealer if that helps? but ask BarryK he'll know for sure and he is a member. What say you barry?
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Old 04-10-2009, 06:19 PM
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No difference? Who ever said that did not know. Check any of the newer technical bulletins for PPG or others. It will list two different grits for prep. One "P" grit and a different US grit version.

For example, the primer I am using now PPG DLV8005 2K A-Chromatic Surfacer LVs says...

Original Paintwork should be sanded using U.S. 240 / European P280 grit discs (dry) or U.S. 320 / European P360 grade paper (wet).

The sealer PPG DLV8085 says, Overcoat / Recoat:After 72 hours, sealer must be sanded. If sanded film isbelow 1 mil, sealer must be reapplied.
Grade wet U.S. 500 / P1000 grade paper
Grade dry U.S. 500 / P1000 grade paper

Huge difference when you get to the finer grits.

Look at the PDF I posted. I shows you the differences. Your P600 is less then a US 400.

Sorry if that is bad news.
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Old 04-10-2009, 07:07 PM
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not really,like I said ,when the paint is on I cant tell and I'm pretty critical about sand scratches,I wet sand with p400 for regular work and go to p600 and 800 for the real nice stuff.It looks good so save yourself all the confusion for the hardstuff. I use fandelli made in mexico its the best paper out there and half the price of 3m,if it matters,I dont know.BarryK. would know,you out there bear? Well the paint supply store said there was no difference but their idiots for the most part sooooooooo,if it looks good who cares,But I'd never Paint anything sanded with 240 or 280 da paper thats for sure.I use 320 or 400 da even on used car work.Anyways my reading and comprehension skills are weak so I only go by what I see not what I read.

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Old 04-10-2009, 08:42 PM
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Quote:
Originally Posted by cboy
Um, just so this thead stays on track...my questions are:

A) Does worn paper sand at a finer grit that when it is new and can that potentially result in adherance problems.

B) How fine a grit can you use before it will hinder adherance of the base coat.

We have pleanty of threads in the archives about the best grit to finish up with. So that isn't my question. I'd like to keep this on just A and/or B above.
A) Yes because im a tightwad also, i use 80G then when it gets old it gets to about 180 or so
B) i use 320 G to block the primer streight, then i block with 500w, thats the finest that i use, only to block now if its all good i just use a red scotch pad to scuff the area


i did a 50 gmc pickup and used a gray scotch pad and we had problems with the paint flaking off, never had a problem with red
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  #38 (permalink)  
Old 04-11-2009, 07:42 AM
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On my very best jobs I sand with 600 then 800 but I change the paper as soon as it stops cutting good ,it doesn't go far two or three sq ft.gray scuff pads are for clear coat and blends only, red is for paint prep but sand first unless you use adheasion promoter the paint will chip and peel easily. Sandpapers cheap compared to labor wasted needlessly. paper does get finer and finer but change them all out when they stop cutting well ,sanding is hard enough cboy.Anyways, I thought that rig was painted by now ,you working on something else already?

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  #39 (permalink)  
Old 04-11-2009, 08:18 AM
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Quote:
Originally Posted by low50s
A) Yes because im a tightwad also, i use 80G then when it gets old it gets to about 180 or so
B) i use 320 G to block the primer streight, then i block with 500w, thats the finest that i use, only to block now if its all good i just use a red scotch pad to scuff the area


i did a 50 gmc pickup and used a gray scotch pad and we had problems with the paint flaking off, never had a problem with red
A) yes the paper gets finer and finer B) 8oo good ,iooo bad if your sanding primer C) but this is no subsitute for experience,add up all the opinions and see for yourself thats what we do.
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  #40 (permalink)  
Old 04-11-2009, 09:48 AM
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the only time i use gray pad is when i do a blend
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  #41 (permalink)  
Old 04-11-2009, 10:01 AM
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Quote:
Originally Posted by low50s
the only time i use gray pad is when i do a blend
Thats what their made for.One other good use is wraping wet paper around them as a soft block, but I'm sure you know that trick.
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Old 06-28-2009, 04:20 PM
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Couple sanding observations.

If you sand with worn paper you are less likely to get a flat surface.

Intuitively, I thought that paint would adhere better as the paper gets courser.
Surprisingly, I saw some test results that showed the opposite.
I suppose there is an optimum grit for adhesion depending on the paint, viscosity, temperature, volatility, etc.

Anyway, I use 600 grit pre BC with good results. I have seen sand scratches on a car that was sanded with 360 grit.
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